This invention relates, generally, to an industrial metal detector having a resonant circuit oscillator and more particular to a proximity detector for sensing any type of metal in motion past its sensing coil while the oscillator maintains a constant present level of oscillation throughout its sensing range.
Prior art proximity detectors using sensor coils are applied to a number of different industrial applications and one group of applications includes the measurement of speeds, flow rates or synchronization of motors or drives. In the synchronization mode, a circular device such as a wheel with protruding teeth thereon rotates past the sensor coil of the detector and produces a sync pulse. In motor speed detection, the detector senses the rotating teeth on the gear. Yet in another detection mode, a flow meter having an impeller with metallic vanes has liquid passing therethrough driving the impellor and rotating the ends of the vanes past the sensor coil producing the sync pulses. For these type of applications, passive and active magnetic sensors are often employed to convert the mechanical motion of ferrous gears and the like into electrical signals. These electrical signals are then translated into the position, revolution per minute and flow rate of the equipment being monitored.
Known passive and active metal detectors are often limited to sensing only the motion of ferrous metals passing across the path of their sensor coils. If such a metal detector incorporated a magnetic sensor then in a flow meter application, there exists the possibility of magnetic drag when it detects the movement of a ferrous impellor. This magnetic drag may cause the impellor to stop its rotary motion at slow flow rates and is further known to create wobbling of the impellor at high flow rates. This will obviously result in inaccurate measurements of the flow rate.
Moreover, prior art metal detectors, especially magnetic ones, are especially susceptible to misalighment in the field by the user due to the critical distance in which the sensor coil must be placed from its ferrous target. In addition, the output signal from a number of magnetic and other metal detectors is subject to run out as the distance between the sensor coil and its ferrous target increases or the target rotates with a wobble. These above critical factors in placement of the sensor coil in relation to its target as well as the dimensional variations in the target itself all contribute to unintelligible signals and inaccurate readings.
An object of the present invention is to provide an improved electronic metal detector which can detect all types of metal both ferrous and non-ferrous which move across its sensor coil.
Another object is to provide an improved electronic metal detector without magnetic drag to influence the accuracy of readings in a flow meter application.
Yet another object is to provide an improved electronic metal detector in which the placement of the sensor coil and the dimensional characteristics of its target are less critical in achieving accurate readings than in previous proximity detectors whether or not of the magnetic sensor type.
A further object is to provide an improved electronic metal detector which corrects for the presence of other metals in its sensing path that are stationary or moving at a slower predetermined rate while still detecting the desired metal target's movement.
A still further object is to provide an improved electronic metal detector capable of using generally any type of oscillator configuration and sensor coil yet sense metal targets over a greater distance from the sensor coil even though stationary metal is between the target and the sensor coil.
Another further object is to provide an improved electronic metal detector which gives a reliable indication that the sensor coil has been damaged by either a shortened or open coil circuit.
Further objects and advantages will become apparent form the following description wherein reference is made to the drawings.